1. Field of the Invention
The present invention relates to a gas seal for a reactor for treating strands or strips of material, in which the reactor has the following features. The invention also relates to a reactor having the gas seal.
The reactor has an outer jacket that extends parallel to the transportation direction of the strands or strips of material, as well as a front wall and a rear wall or an upper and a lower seal wall. Either the front wall or the rear wall or the front wall and the rear wall or either the upper or the lower seal wall or both seal walls have at least one opening for the introduction of at least one strand of material or strip of material and/or at least one opening for the removal of at least one strand of material or strip of material.
The reactor has devices for the transportation of strands of material or strips of material through the reactor and devices for transporting strands of material or strips of material to the reactor and for transporting strands of material or strips of material from the reactor.
The reactor has devices for heating the reactor interior or parts thereof and/or for heating strands of material or strips of material or parts thereof or for cooling the reactor interior or parts thereof and/or strands of material or strips of material or parts thereof, or does not have such devices.
The reactor has devices for supplying temperature-regulated or non temperature-regulated gases to the reactor space and/or for removing gases from the reactor space.
The reactor has, at those places at which at least one strand of material or strip of material enters the reactor space and/or at which at least one strand of material or strip of material leaves the reactor space, through openings, a gas feedline and distribution device with gas discharge openings. The distribution device allows gas to flows out at these openings for the material inlet or outlet to generate a gas curtain. The gas curtain prevents the penetration of undesirable substances into the reactor space as well as the exit of undesirable substances from the reactor space.
For the treatment of endless strands of material or strips of material, for example at elevated temperatures under continuous operation, reactors are used through which this endless material is drawn by transportation devices. Generally, the transportation devices can be motor-driven and velocity-regulated uncoiling and coiling devices generally provided with rollers. The strands or strips are in this connection either drawn only once or, which is more often the case, are drawn several times in succession through the reactor. In the latter case for reasons of the economy of the process, the strands or strips of material are, after the first passage through the reactor, fed again immediately into the reactor generally by reversing rollers and are transported once more through the reactor. This operation is repeated as often as required by the process procedure. In many cases, the reactors not only constitute equipment in which the strands or strips are subjected to specific temperatures for the execution of desired physical procedures, but also chemical reactions proceed in parallel to the temperature treatments, for the execution of which reactions reactants, generally in gaseous or vapor form, are often introduced into the reactor and, after a specific residence time, are removed from the reactor, possibly together with resulting reaction products. If the gas space in the interior of the reactor contains gases or vapors that are toxic or corrosive or that for other reasons must not be discharged into the atmosphere surrounding the reactor, all the inlets and outlets at which the strands or strips of material are conveyed into the reactor or are conveyed from the reactor must be sealed so that no harmful or negative effects on humans, material or the environment outside the reactor can take place.
Several technical solutions to this problem exist. For example, gas-lock boxes may be employed at the material inlets and outlets from which the gases and vapors leaving the reactor are removed by suction and are then rendered harmless. However, due to their bulk, such gas-locks interfere with the outlet or inlet openings for the strands or strips of material, and a further disadvantage is the fact that, in order reliably to remove the harmful substances, large amounts of foreign or ballast gases have to be sucked into the gas-lock and then handled. In addition, part of the gases and vapors present in the interior of the reactor is sucked into the gas-lock space and is then lost for purposes of reutilization and/or recycling. The latter disadvantage applies to gas-lock spaces operating under reduced pressure. Gas-locks operating under an excess gas pressure occupy even more space than “reduced pressure gas-locks” because, with this solution, the reversing rollers for the strands or strips of material have to be located within the gas-lock chamber. If this were not the case and if for example the gas-lock chambers had through passages for the strands and strips of material, some of the harmful substances would undesirably exit through these passages. In addition, in the case of “excess pressure gas-locks” the strands or strips of material may possibly not be visually checked or checked only inadequately. Then, the operating workforce can no longer carry out directly and/or cannot carry out sufficiently rapidly the control, regulatory, and preventative interventions on the strands or strips that are necessary with the processes taking place in the reactors. In another type of procedure so-called gas curtains are employed. In this case, at the openings at which the strands or strips of material are transported into the reactor or are transported from the latter, a harmless gas is blown through suitable openings or nozzles into the furnace openings and onto the strands or strips of material in such a way that a gas flow is produced that is directed substantially into the interior of the furnace and, in the manner of a dynamic curtain, prevents the harmful gases and vapors from leaving the reactor.
As will be shown hereinafter, the hitherto known seals using gas curtains also do not operate satisfactorily.
U.S. Pat. No. 5,928,986 to Parmentier et al. describes a furnace for the oxidizing activation of the fiber surfaces of carbon fibers or yarns in the carbonized state with a suitable gas at temperatures of 800° to 1000° C. At the inlet opening and the outlet opening for the strand of material, the furnace has gas-lock chambers that are equipped with cooling and suction systems. The gases leaving the furnace and entering the gas-lock chambers are sucked out via the suction systems and rendered harmless. According to another technical variant, an inert gas can be blown into the gas-lock chambers. This inert gas serves to generate a gas curtain there and prevent the uncontrolled penetration of air into the interior of the furnace. This gas, too, is for the most part sucked out from the gas-lock chambers. Here, in each case too, gas-lock chambers are therefore involved whose gaseous contents are sucked out. In the first case the gas leaving the furnace and in the second case a rinsing gas that is introduced into the gas-lock chambers are sucked out together with the gases originating from the furnace. If in this case a gas curtain is generated at all, then it occurs in a gas-lock chamber and not at the actual entry to the working space of the furnace.
German Published, Non-Prosecuted Patent Application No. DE 33 12 683 A1 discloses a vertical throughflow furnace for the production of carbonized carbon fibers from so-called preoxidized fibers. The production process is carried out in the temperature range from 300° to 1500° C. The preoxidized fibers required for the execution of the process are produced in an upstream process stage by treating organic fibers, made from for example polyacrylonitrile, at temperatures of up to 300° C. The fibers are infusible. The treatment of the fibers in the carbonization furnace takes place under a protective gas. For this, protective gas is blown in at the lower material outlet of the furnace in a manner not described in more detail, the gas rising upwardly in the furnace. Provided in the vicinity of the heating zones, which are located at a relatively large distance from the inlet and outlet openings for the fiber strip, are nozzles through which nozzles temperature-regulated protective gas is blown in so that a gas curtain is generated within the heating chambers or heating zones. Just underneath these nozzles are installed suction openings. A large part of the blown-in protective gas that is now charged with gaseous and vaporous reaction products from the carbonization process is removed through the suction openings. The purpose of this gas curtain is to prevent harmful, in particular tar-containing decomposition products, flowing upwardly within the vertical furnace into the cooler, upper furnace zones. The furnace should thereby not be sealed against the outside.
A gas curtain that is operated at the material entry points and outlets of the furnace and thus not directly in its reaction space and that does not employ gas-lock chambers has been described in U.S. Pat. No. 6,027,337 issued to Rogers et al. The furnace is used for the production of carbon fibers from polyacrylonitrile fibers, preferably for the production of preoxidized and thus non-meltable fibers in the temperature range from ca. 150° to 300° C. In this connection, the fibers are exposed to an air current. In the reactions that thereby take place, very poisonous gases such as hydrogen cyanide or carbon monoxide are also released, in addition to steam and carbon dioxide, and must in no event, and not even in very small amounts, pass untrapped into the space outside the furnace. The technical solution employed here provides an air feedline and distribution device that is equipped with outlet openings for the air, specifically with wide slit-shaped nozzles, at each point at which a material strip is transported into or transported from the furnace. In order to generate the gas curtain that is intended to seal the interior of the furnace against the external atmosphere, gas is blown through these nozzles at a specific angle in the direction of the interior of the furnace. An air current that is overwhelmingly directed into the interior of the furnace and that acts as a gas curtain is thereby formed at the side of the openings for the fiber strands or fiber strips facing the interior of the furnace. This technical solution too unfortunately does not completely fulfill its expectations for it has been found in everyday operational use that the concentrations of harmful gases in the vicinity of the inlet and outlet openings for the strips of material were too large.